1.Field
This invention relates to thin metal alloy films which are quasicrystalline or approximately quasicrystalline, as opposed to amorphous or crystalline, in nature. It is particularly directed to a method for making very thin such films from materials having the general formula Al.sub.a Cu.sub.b Fe.sub.c X.sub.d I.sub.e, where X represents one or more optional alloy elements and I represents manufacturing impurities. It is further directed to applications which take advantage of the unique properties of such films.
2. State of the Art
Alloy metal films are well known. Alloys having the general formula Al.sub.a Cu.sub.b Fe.sub.c X.sub.d I.sub.e, where X represents one or more elements selected from the group consisting of V, Mo, Ti, Zr, Nb, Cr, Mn, Ru, Rh, Ni, Mg, W, Si and the rare earth elements, and I represents manufacturing impurities, generally present in an amount of less than two percent of the atoms present, are disclosed, for example, by U.S. Pat. No. 5,204,191. U.S. Pat. Nos. 4,595,429 and 4,710,246 disclose a number of Aluminum-based alloys characterized by amorphous or microcrystalline structures.
An icosahedral phase was observed in 1984 in a rapidly quenched AlMn alloy. Since that time, many experiments have been carried out to clarify the structure and properties of this new ("quasicrystalline") state of condensed matter. Most of the quasicrystalline phases studied have been metastable; however, a few of them have evidenced thermodynamic stability. The AlCuFe alloys, for example, provide pure icosahedral phases of high structural quality and peculiar electronic and magnetic properties. Notably, such alloys are characterized by unusually high electrical resistivity values, which increase as the structural quality of the sample is improved; a very low thermal conductivity; a low density of states at the Fermi level; a strong composition dependence of the resistivity and the Hall coefficient and a diamagnetic susceptibility.
The AlCuFe alloys have typically been prepared either by melt spinning or long term annealing of bulk ingots. Monograins of millimeter size have been produced by these techniques. Recently, films about 10 .mu.m in thickness have been obtained by cosputtering three elements onto liquid nitrogen cooled substrates and then annealing the resulting films. Binary metastable quasicrystals have also been produced by solid state diffusion of either sputtered or evaporated layers. Decagonal Al.sub.3 Pd phases have been obtained by the lateral diffusion of Al islands on a Pd thin film.